Regarding the First Invention
A layered product comprising resin thin film layers and metal thin film layers are used in a wide range of applications, for example, as a magnetic recording medium such as a magnetic tape, a wrapping material or an electronic component.
The resin thin film layers used in such a layered product are manufactured by melting and stretching a resin material into a self-supported film or by applying a solution of a resin material diluted with a solvent to a supporting base and drying the resin for curing. However, the resin thin film layers obtained by the former method are provided with slight roughness on a surface of the film for a small coefficient of friction by allowing a protrusion forming component (e.g., externally added particles) to be contained in the film in order to provide the film with the conveyance properties. Moreover, the former method tends to require large scale equipment to manufacture the resin thin film layers. On the other hand, the resin thin film layers obtained by the latter method may have large protrusions on the surfaces thereof caused by defects generated in the coating film after drying. Moreover, some solvent may cause environmental problems. Furthermore, the smallest thickness of the resin thin film obtained by the above methods is only 1 μm, and neither of the above methods can produce thinner thin films stably.
To obtain thin resin layers stably, a method of forming a resin thin film on a supporting base in a vacuum has been proposed. In this method, a resin thin film is evaporated in a vacuum and adhered to a supporting base to produce thin films. It is said that this method allows resin thin films to be formed with relatively small equipment that less adversely affects the environment.
On the other hand, for formation of metal thin film layers, a method of vacuum evaporation on a surface of a base that is moving at high speed is advantageous for mass production and is put in industrially practical use. The thickness of the metal thin film layer produced by this method is very thin, so that the shape of the surface of the base is reflected exactly on the surface of the metal thin film.
The recent needs for a layered product including resin thin film layers and metal thin films are directed to further degrees of compactness and high performance. Therefore, the tendency of forming thinner resin thin films and metal thin films and eliminating factors causing instability such as abnormal protrusions or foreign substances is increasingly strengthened.
However, the layered product obtained by forming a metal thin film layer, for example by evaporation, on a resin thin film layer obtained by melting and stretching a resin material, or applying a solution of a resin material diluted with a solvent to a supporting base and drying for curing have the following disadvantages. The resin thin films cannot have a small thickness, and may contain foreign substances or have protrusions inhibiting various characteristics on the surface thereof. Thus, a layered product that can satisfy the need for thinness and high performance has not been obtained.
Furthermore, a layered product comprising metal thin film layers formed, for example by evaporation on resin thin film layers formed on a supporting base in a vacuum can have a small thickness. However, the surface characteristics are not sufficient so that various characteristics are not stable. Thus, this layered product cannot satisfy the characteristics strictly required by the current need.
Regarding the Second Invention
The current need for compactness and high performance of electronic components is increasingly strengthened, and this is the case for capacitors as well. The capacitance of the capacitor is in proportion to the area of the dielectric and in inverse proportion to the square of the thickness of the dielectric layer when the dielectric constant of the dielectric is the same. Therefore, in order to achieve a compact capacitor and maintain or increase the capacitance thereof, it is effective to make the dielectric layer thin and increase an effective area of a region where capacitance is generated.
One known example of a layered product comprising dielectric layers and metal thin film layers used for electronic components such as capacitors is a layered product for a film capacitor. This layered product is formed by layering or winding a metallized film obtained by depositing a metal thin film such as aluminum on a resin film such as polyester (e.g., PEN, PET), polyolefin (e.g., PP) or PPS by vacuum evaporation, sputtering or the like.
However, there is a limit for the thickness of the resin film due to various constraints such as handling properties or processability of the film during or after production. The thickness of currently used film capacitors can be as small as about 1.2 μm. Therefore, in order to increase the capacitance of the capacitors further, it is necessary to increase the effective area of the capacitance generation portion, namely, increase the number of times of layering or winding. However, this contradicts the requirement for compactness of the capacitor. In other words, for film capacitors, the achievement of high levels of both compactness and large capacitance has reached the limit at the moment.
On the other hand, a layered product for a capacitor comprising a dielectric layer and a metal thin film layer produced by a method totally different from that for the conventional film capacitor, which allows the thickness of a dielectric layer to be about 1 μm, has been proposed (U.S. Pat. No. 5,125,138). The layered product has the same layered structure where dielectric resin layers and metal thin film layers are deposited sequentially as the conventional layered product for layered type film capacitors. However, the layered product has about 1000 depositions or more and has a thickness on the order of several mm.
However, the examination by the inventors of the present invention revealed that various problems arise in production of a capacitor with such a layered product in the same manner as with the conventional layered product for layered type film capacitors.
For example, when thermal load or external pressure is applied to the layered product in a pressurizing and heating press process during production of the layered product or a process for mounting a capacitor formed of the layered product on a printed circuit board or the like, the layered product is damaged easily. Furthermore, in order to use the layered product as a capacitor, it is necessary to form external electrodes on the sides of the layered product. Conventionally, for the layered type film capacitors, the external electrodes are formed by metal spraying. When this technique is applied to the above-described layered product, the adhesion strength between the metal thin films and the external electrodes is poor so that failure of electrical connection or falling of the external electrodes may occur.
It has turned out that these problems become more serious when the thickness of the dielectric layer is made even smaller to the extent that cannot be achieved for the conventional film capacitor. These problems cannot be avoided to achieve compactness and high capacitance of a capacitor with the above-described layered product.